Lamp



L. RIVIER Nov. 20, 1934.

LAMP

Filed Nov. 5, 1932 I )NV/VTOR MW W Patented Nov. 20 1934 UNITED STATES PATENT OFFICE.

Application Novembe; s, 1932, Serial No. 641,083

In Switzerland November 16, 1931 1 Claim.

The present invention relates to lamps and more particularly to lamps comprising a bulb of which a portion is silvered or otherwise rendered specular so that the luminous flux of the I light source is emitted in certain desired directions only.

An object of the invention is the provision of a lamp of the preferred type in which the specular portion of the bulb is constituted by an 0 ellipsoid or revolution.

.A further object is the provision of a lamp in which the specular portion of the bulb is constituted by an ellipsoid of revolution and the transparent portion has such a shape that one of the foci of the specular portion is situated outside the bulb.

These and other objects will appear more fully from the detailed description of the accompanying drawing, in which,

Figures 1 to 4 show each a diagrammatic representation of a lamp according to the invention.

According to Figure l, the bulb 1 is provided with a specular portion 2 and with a transparent portion 3. The specular portion has the shape of a fragmentary ellipsoid of revolution of which the two focal points are indicatedat 4 and at 5. The transparent portion 3 of the bulb is of spherical shape and has its center preferably situated in the focus 5 so that the rays which are concentrated through this focus will leave the bulb Without any aberration.

The circle '7 drawn about the focus 4 is supposed to indicate the actual size of a light source placed in the focus, or the material source, in contrast to the theoretical source which is supposed to coincide with the focus. Practically, light rays will be emitted from any point of this circle. The rays a which coincide with a radius vector of the ellipsoid are concentrated through the focus 5 and leave the bulb through the transparent portion. The rays 1) which are emitted in a direction tangential to the circle '7 4 are reflected by the portion 2-in such a direction as to be tangential to a circle 8 about the focus 5. This circle is larger than the circle 7 for such rays which strike on the reflector 2 at the inner side relative to a plane extending at right angles to the main axis of the ellipsoid and through the center thereof between the two focal points.

In the modification shown in Figure 2, the reflecting elliptical portion 2a. of the bulb la is more elongated, so that a larger number Of light rays are permitted to strike the reflector at the outer side thereof relative to the above defined plane, this plane being indicated at 9 in Fig. 2. Rays bi, emitted according to a tangent from the circle 10 representing the filament, and striking the reflector at its place of intersection with the plane 9 are reflected tangentially to a circle 11 about the focus 5a and of a diameter equal to that of the circle 10. Rays in striking the reflector on the outside of the plane 9 are reflected tangentially to a smaller circle 12, and the rays b3 striking the reflector 2a on the inside of this plane 9 are reflected tangentially to a larger circle 13.

The modifications according to Figs. 3 and 4 show that one of the focal points of the ellipsoid can be situated outside the light bulb.

In Fig. 3, the elliptical portion 21) of the bulb ID has two focal points 4b and 6. In order to place the focus 6 on the outside of the bulb, the transparent portion 3b projects into the elliptical portion of the bulb. .The curvature of the transparent portion is preferably spherical so that the rays can normally traverse this portion. An opaque zone 14 may be provided to separate the reflecting and the transparent portion.

In Fig. 4, the two focal points of the reflecting portion 20 of the bulb are indicated at 40 and 6a. Owing to the elongated shape of the ellipsoid having the focal points near the ends of the major axis, it is' possible to give the end 30 of the bulb 1c the same shape as to that of an ordinary light bulb, while the focus 6a is outside of the glass of the'bulb. The transparent end of the bulb can be flattened, more or less convex, and even spherical without the focus 6a falling in the interior of the bulb, and notwithstanding the fact that the solid angle of the luminous flux reflected by the ellipsoid is considerable.

In all the bulbs shown, the specular fragmen of an ellipsoid of revolution has its opposite ends limited by circles 15 and 16, the end 16 being fixed to the cap 17 of the lamp. The focus in. proximity of which is placed the light source is situated between the two circular ends of the' fragment of the ellipsoid.

An advantage of the lamps according to Figs. 3 and 4 consists in the fact that the luminous flux is utilized at well determined conditions, and in the fact that the image of the light source can have more advantageous properties than the real source in so far as the shading 0r intrinsic brightness of the light is concerned.

' The brightness can be more intense in the ter of the image of the light source than in its cenperiphery and can increase from the towards the center. I

The fact that an image of the light source is formed-in the second focus permits a screen to be disposed so that an edge of the screen passes through the focus 5 or 6 and the screen then intercepts all light rays passing on a certain side of the focus.. Such an arrangement can be utilized for anti-glare vehicle head lights and the provision of such a screen is facilitated in lamps according to Figs. 3 and 4 where the second focus is outside of the glass of the bulb..

These bulbs present still other advantages. A great number of rays are concentrated near the focus 6 or 6a and the heat received by a body placed in close proximity of the focus is intense. Such a bulb can accordingly be used as ignition device to replace matches or other lighters.

The bulb having one of the foci outside of the glass can be used for the purpose of decorative illumination. The bulb can be hidden behind a surface for instance on the ceiling of a room to be illuminated and can be mounted in a protecting sleeve carrying the lamp socket which is connected to the electric light mains.

In the case of the bulbs having one focus of the reflector outside the glass, a brilliant metal body or other reflector can be combined with the focus and this metal body can have various shapes according to the desired lighting effects. This body can be a fragment of a paraboloid. It can also be constituted by a small metal or periphery glass disk which may be polished or dull and rotatable about an axis so as to be able to direct the maximum of light flux in a desired direction. This body can be colored and thereby color the light which it reflects or diffuses. It may have a plurality of faces of different color so that the color of the light reflected or diffused may be varied by changing the position of the body. When reflected or diffused by metal surfaces,

the color of the light will be paler than when The lamp according to Figs. 3 and 4 with one focus outside thereof can be used also with advantage in all cases of an illuminating device comprising a condensator or a projection objective, owing to the .fact that a greater part of the emitted light can be utilized and this light is concentrated to a focus.

In this case the shadow cone, resulting from the filament support and because the rear part of the bulb where the glass is flxed to the socket cannot be used as ellipsoidal reflector, can be suppressed by various means, for instance by a, suitably shaped filament or by its position relative to the first focus, or by the addition of a convergent lens placed in the shadow cone in front of the bulb in such a manner that the periphery of the lens is tangent to the surface of the cone, and that the lens receives directly from the light source a pencil of rays which it can concentrate to the exterior focus of the ellipsoid.

I claim:-

In an electric lamp, a bulb having a cap, said bulb being formed as surface of revolution, a portion of which next the cap having the shape of a fragment of an ellipsoid, a second portion of the bulb surface projecting inwardly into the bulb to form an exterior cavity'in the bulb surface, a third portion of the bulb surface forming a connecting surface between said ellipsoidal portion and the inwardly projecting portion of the surface, and a source of radiant energy placed in a focus of the ellipsoidal bulb portion in the interior of the bulb, a conjugate focus of the ellipsoidal bulb portion being situated outside of the bulb, the entire inwardly projecting portion of the bulb surface being transparent and extending between said two foci, and the entire ellipsoidal portion of the bulb surface forming a reflector for reflecting the rays issued by said L15 LOUIS RIVIER.

the body consists of a mirror made of colored glass. 

